Summary of Work: DNA Polymerase b (pol b ) produces a nuclear protein which is important in short gap filling during DNA repair. Deletions of 8p, which include the pol b locus, are frequent in bladder tumors (25 percent) and lung tumors (40 percent). Early reports implied pol b may be mutated in several human cancers including colorectal, prostate, and bladder. However, subsequent reports suggested these changes may actually be alternative splice variants of pol b. The hypothesis for this project is that Pol b is frequently mutated in bladder and lung cancers, particularly in response to environmental exposure and that splice variants and inherited polymorphisms in this gene may increase susceptibility to bladder and lung cancers. We screened the genomic DNA of 8 human bladder cancer cell lines, 11 primary bladder tumors, and 9 primary lung tumors for mutations in exons 1 through 14 and exon a of pol b by SSCP analysis. We detected a heterozygous intron 13 change in 0 of 8 bladder cancer cell lines, 3 of 11 (27%) bladder tumors and 3 of 9 (33%) lung tumors. Direct sequence analysis revealed an insertion of a thymidine into a string of five thymidines 17 base pairs prior to the beginning of exon 14. In screening 32 additional bladder cancer cases and 31 additional controls, we have shown the intron 13 insertion to be present in 21.9% cases and only 9.7% controls. Ongoing is an attempt to determine if this trend is significant. We detected a CCC to CGC transversion at codon 242 in one bladder cancer cell line which would result in a proline to arginine amino acid substitution. In a collaboration with Dr. Sam Wilson, we will look at the expression and activity of pol b in this cell line for environmentally-associated bladder cancer, and inherited variants of this gene or splice variants may affect susceptibility to this common cancer.